Loudspeaker with a first and a second diaphragm body

ABSTRACT

Loudspeaker provided with a frame ( 2 ), a diaphragm ( 4 ) and an electric driving means for moving the diaphragm along an axis of translation ( 8 ) with respect to the frame. The diaphragm runs round the axis of translation and includes an outer conical first diaphragm body ( 4 A) and an inner conical second diaphragm body ( 4 B) which is invertedly oriented with respect to and positioned inside the first diaphragm body. These bodies each have a base portion and a top portion, the top portion ( 4 At) of the first diaphragm body and the base portion ( 4 Bb) of the second diaphragm body being interconnected. The diaphragm is suspended from the frame through a first flexible suspension means ( 14 ) extending between the base portion ( 4 Ab) of the first diaphragm body and the frame and through a second flexible suspension means ( 16 ) extending between the top portion of the first diaphragm body and the frame. The top portion ( 4 Bt) of the second diaphragm body is attached to a movable part ( 6 M) of the driving means. Due to this suspension arrangement in combination with the specific form of the diaphragm a very small height of the loudspeaker is within reach.

The invention relates to a loudspeaker provided with a frame, adiaphragm and an electric driving means for moving the diaphragm alongan axis of translation with respect to the frame, which diaphragm runsround the axis of translation and includes an outer conical firstdiaphragm body and an inner conical second diaphragm body which isinvertedly oriented with respect to and positioned inside the firstdiaphragm body, each body having a base portion and a top portion, thetop portion of the first diaphragm body and the base portion of thesecond diaphragm body being interconnected, and which electric drivingmeans includes a stationary part connected to the frame and a movablepart.

JP-A 0 820 52 83 discloses a loudspeaker having a diaphragm including anoutside cone part and an inverted inside cone part coupled in a couplingpart to the outside cone part. A voice coil bobbin is joined to theinside cone part. The diaphragm is suspended from a frame by means of aflexible suspension ring fixed to the largest circumferential rim of theoutside cone part and the frame and a flexible centering elementattached to the frame and a middle portion of the voice coil bobbin.Although due to the applied diaphragm the height of the knownloudspeaker may be smaller than the height of generally knownloudspeakers provided with single conical diaphragms, this known speakerhas still a relatively large height owing to the required relativelylong voice coil bobbin.

It is an object of the invention to improve the loudspeaker as definedin the preamble in such a way that a very small height is within reach.

This object is achieved by the loudspeaker according to the invention,which is provided with a frame, a diaphragm and an electric drivingmeans for moving the diaphragm along an axis of translation with respectto the frame, which diaphragm runs round the axis of translation andincludes an outer conical first diaphragm body and an inner conicalsecond diaphragm body which is invertedly oriented with respect to andpositioned inside the first diaphragm body, each body having a baseportion and a top portion, the top portion of the first diaphragm bodyand the base portion of the second diaphragm body being interconnected,and which electric driving means includes a stationary part connected tothe frame and a movable part, wherein the diaphragm is suspended fromthe frame through a first flexible suspension means extending betweenthe base portion of the first diaphragm body and the frame and through asecond flexible suspension means extending between the top portion ofthe first diaphragm body and/or the base portion of the second diaphragmbody on the one hand and the frame or a mechanical structure fixed tothe frame on the other hand and wherein the top portion of the seconddiaphragm body is attached to the movable part of the driving means. Dueto this suspension arrangement the moving part of the driving means ofthe loudspeaker can be surprising short, i.e. the axial dimension of themoving part, thus the dimension considered along the axis oftranslation, can be small. This means that the required built-in depthis also small. For this reason the loudspeaker according to theinvention is very suitable for applications in which flat devices aredesired or required. Such applications can be found e.g. in theautomotive field.

In a practical embodiment the driving means is positioned opposite tothe second diaphragm body and at least partly inside the first diaphragmbody. Generally, the stationary part of the driving means, also referredto as electromagnetic actuator, includes a magnetic yoke with apermanent magnet and the movable part of the driving means includes adriving coil, also referred to as voice coil, for magneticalco-operation with the magnetic yoke. Thus, the driving coil is situatedin the magnetic field of the magnet.

A preferred embodiment of the loudspeaker according to the invention ischaracterized in that the first flexible suspension means is attached tothe first diaphragm body on the one hand and the frame or a mountingelement fixed to the frame on the other hand.

The first flexible suspension means may be a flexible structure with anundulation or wrinkle. Such a structure may be, for example, acorrugated rubber annular rim.

In general the second flexible suspension means is a radial bearingmeans, also referred to as centring means, particularly centring ring orspider. This means serves to guarantee an accurate alignment of thediaphragm with respect to the frame and may be in the form of a flexiblestructure of, for example, rubber, synthetic material and/or textile.

A further preferred embodiment of the loudspeaker according to theinvention is characterized in that the second flexible suspension meansis attached to the first and/or second diaphragm body on the one handand the frame or the mechanical structure fixed to the frame on theother hand. In this context it is noted that mechanical structure is astiff structure which may include a mounting element that may be securedto or include the stationary part of the driving means. Preferably, themounting element comprises a central support located at the axis oftranslation of the diaphragm and at least partly positioned inside thediaphragm.

Although the diaphragm can be constituted by two separate diaphragmbodies, it may be favourable, for example for manufacturing reasons, ifthe first diaphragm body and the second diaphragm body form an integraldiaphragm body. The material of the diaphragm may be conventionalpressed paper, injection molded plastics or deep-drawn plastics, such aspolycarbonate, polypropylene.

The invention also relates to a loudspeaker unit provided with anenclosure and a built-in loudspeaker according to the invention.

With reference to the claims, it is to be noted that variouscharacteristic features as defined in the set of claims may occur incombination.

The above-mentioned and other aspects of the invention are apparent fromand will be elucidated, by way of non-limitative example, with referenceto the embodiments described hereinafter.

In the drawings:

FIG. 1 shows a first embodiment of the loudspeaker according to theinvention in a diagrammatic cross-section,

FIG. 2 shows a second embodiment of the loudspeaker according to theinvention in a diagrammatic cross-section and

FIG. 3 shows a third embodiment of the loudspeaker according to theinvention in a diagrammatic cross-section.

The electrodynamic loudspeaker according to the invention, shown in FIG.1, includes a frame or chassis 2, a diaphragm 4 and an electromagneticactuator 6 for moving the diaphragm 4 along an axis of translation 8with respect to the frame 2. The diaphragm 4 comprises two conicalbodies, viz. an outer conical first diaphragm body 4A and an innerconical diaphragm body 4B which bodies are invertedly oriented withrespect to each other. The first diaphragm 4A has a base portion 4Ab anda top portion 4At. The second diaphragm 4B has a base portion 4Bb and atop portion 4Bt, the top portion 4At and the base portion 4Bb beingmutually connected. In this example the conical bodies 4A and 4B form anintegral whole, i.e. the diaphragm 4, the top portion 4At and the baseportion 4Bt coinciding. The actuator 6, which is also referred to aselectric driving means in this document, includes a stationary part 6Sconnected to the frame 2 and a movable part 6M connected to thediaphragm 4. The stationary part 6S, which is fixed to a mounting plate2A of the frame 2 by means of e.g. folding, has a magnetic yoke 6S1 anda permanent magnet 6S2. Due to the space 5 created by the diaphragm 4 arelatively large stationary part 6S can be applied, so that not onlycompact, expensive neodymium magnets, but also conventional and thuscheap magnets of e.g. ferrite can be used. The movable part 6M, which istranslatable along the axis 8 with respect to the stationary part 6S,has a driving coil 6M1, also referred to as voice coil, and a tubularcoil support 6M2 supported by the coil 6M1. Upon energization thedriving coil 6M1 magnetically co-operates over an air gap 10 with themagnet 6S2. The coil support 6M2 has an end portion 12 which is situatedoutside the gap 10. The top portion 4Bt of the second diaphragm body 4Bis attached to this end portion 12 by means of e.g. an adhesive. Thediagram 4 is suspended from the frame 2 by means of a flexiblecorrugated annular rim 14 of e.g. rubber, which rim is also referred toin this document as first flexible suspension means. The rim 14 isattached to the base portion 4Ab of the diaphragm body 4A, e.g. by meansof an adhesive, and is further fixed to the frame 2. An undulatingcentring spider 16, also referred to as second flexible suspension meansin this document, is provided in or near the plane defined by the topportion 4At of the first diaphragm body 4A and the base portion 4Bb ofthe second diaphragm body 4B. The spider 16 is attached to the diaphragm4, at the location of the top portion 4At and the base portion 4Bb, bymeans of e.g. an adhesive. The spider 16 is further fixed to a centralmounting element 18. This mounting element 18 is fixed to thesoft-magnetic yoke 6S1 and via this yoke 6S1 secured to the frame 2.Thus, the mounting element 18 and the yoke 6S1 together form a stiffmechanical structure fixed to the frame 2. The frame 2 may be secured toa wall 20 of a loudspeaker box or a built-in opening.

From FIG. 1 it will be clear that the backside of the loudspeakeraccording to the invention is formed by the second flexible suspensionmeans. The front side of the loudspeaker may be provided with soundapertures 22, which may be covered by a grid 24, a piece of fabric orsomething like that.

Reference is now made to the FIGS. 2 and 3. The features of theembodiments of these Figures which are identical to the correspondingfeatures of the embodiment of FIG. 1 are allocated the same referencenumerals and will not be further described in detail.

In the loudspeaker according to the invention shown in FIG. 2 the frame2 is provided with a concave mounting plate 2A to with the stationarypart 6S of the actuator 6 is secured. This alternative constructionprovides a space 30 in which the stationary part 6S of different typescan be accommodated, without the necessary to adapt other parts of theloudspeaker. The second flexible suspension means 16 extends between thetop portion 4At (or the base portion 4Bb) and a frame 2B of the frame 2and is fixed to the portion 4At (or 4Bb) and the frame part 2B. Electricwires 32 are led along the second conical diaphragm body 4B and fixed toelectric contact elements 34 which are insulated from and secured to theframe 2. A dust cap 36 is provided for acoustical reasons and forprotection the gap 10 against unwanted particles.

The loudspeaker shown in FIG. 3 is provided with electric contact lips34 attached to the central mounting element 18. The mounting element 18is mounted in the yoke 6S1 and via the stationary part 6S secured to theframe 2. Flexible current conductors 36, which are integrated in theundulating structure of the second suspension means 16, are soldered tothe lips 34 and the coil 6M1. These integrated conductors 36 are ratherinsensible to damages.

It is to be noted that the invention is not restricted to theembodiments disclosed. For example, the diaphragm 4 may be made from twoseparate conical bodies 4A and 4B which are joined together duringmanufacture in such a way that their portions 4At and 4Bb are fastenedto each other, e.g. by means of a glue.

1. Loudspeaker provided with a frame, a diaphragm and an electricdriving means for moving the diaphragm along an axis of translation withrespect to the frame, which diaphragm runs round the axis of translationand includes an outer conical first diaphragm body and an inner conicalsecond diaphragm body which is invertedly oriented with respect to andpositioned inside the first diaphragm body, each body having a baseportion and a top portion, the top portion of the first diaphragm bodyand the base portion of the second diaphragm body being interconnected,and which electric driving means includes a stationary part connected tothe frame and a movable part, wherein the diaphragm is suspended fromthe frame through a first flexible suspension means extending betweenthe base portion of the first diaphragm body and the frame and through asecond flexible suspension means extending between the top portion ofthe first diaphragm body and/or the base portion of the second diaphragmbody on the one hand and the frame or a mechanical structure fixed tothe frame on the other hand, and wherein the top portion of the seconddiaphragm body is attached to the movable part of the driving means. 2.Loudspeaker as claimed in claim 1, wherein the driving means ispositioned opposite to the second diaphragm body and at least partlyinside the first diaphragm body.
 3. Loudspeaker as claimed in claim 1,wherein the stationary part of the driving means includes a magneticyoke with a permanent magnet and the movable part of the driving meansincludes a driving coil for an electromagnetical cooperation with themagnetic yoke.
 4. Loudspeaker as claimed in claim 1, wherein the firstflexible suspension means is attached to the first diaphragm body on theone hand and the frame or a mounting element fixed to the frame on theother hand.
 5. Loudspeaker as claimed in claim 1, wherein the secondflexible suspension means is a radial bearing means.
 6. Loudspeaker asclaimed in claim 1, wherein the second flexible suspension means isattached to the first and/or second diaphragm body on the one hand andthe frame or the mechanical structure fixed to the frame on the otherhand.
 7. Loudspeaker as claimed in claim 6, wherein the mechanicalstructure includes a mounting element secured to the stationary part ofthe driving means.
 8. Loudspeaker as claimed in claim 6, wherein themounting element comprises a central support located at the axis oftranslation of the diaphragm and at least partly positioned inside thediaphragm.
 9. Loudspeaker as claimed in claim 1, wherein the firstdiaphragm body and the second diaphragm body form an integral diaphragmbody.
 10. Loudspeaker unit provided with an enclosure and a built-inloudspeaker according to claim 1.